How do I Make a Spawner for Enemies in my Game?
As non-python solution I suggest following:


create an action with location keys. Each frame the action should contain a single spawn position. e.g frame 1 = position 1, frame 2 = position 2 ...
when you want to spawn an enemy 

2.a. create an random integer number in a property via random actuator.

2.b you play the action frame at the emitter (empty) via Action Actuator in property mode (using the random property).

2.c with a collision/ray/near/radar sensor check if the spawn point is empty. If so add an enemy and continue with 2. If not continue with 2.a